erro-silicon, made by heating a mixture
of iron ore, sand and coke in the electrical furnace, is used as a
deoxidizing agent in the manufacture of steel.

Since silicon has been robbed with difficulty of its oxygen it takes it
on again with great avidity. This has been made use of in the making of
hydrogen. A mixture of silicon (or of the ferro-silicon alloy containing
90 per cent. of silicon) with soda and slaked lime is inert, compact and
can be transported to any point where hydrogen is needed, say at a
battle front. Then the "hydrogenite," as the mixture is named, is
ignited by a hot iron ball and goes off like thermit with the production
of great heat and the evolution of a vast volume of hydrogen gas. Or the
ferro-silicon may be simply burned in an atmosphere of steam in a closed
tank after ignition with a pinch of gunpowder. The iron and the silicon
revert to their oxides while the hydrogen of the water is set free. The
French "silikol" method consists in treating silicon with a 40 per cent.
solution of soda.

Another source of hydrogen originating with the electric furnace is
"hydrolith," which consists of calcium hydride. Metallic calcium is
prepared from lime in the electric furnace. Then pieces of the calcium
are spread out in an oven heated by electricity and a current of dry
hydrogen passed through. The gas is absorbed by the metal, forming the
hydride (CaH_{2}). This is packed up in cans and when hydrogen is
desired it is simply dropped into water, when it gives off the gas just
as calcium carbide gives off acetylene.

This last reaction was also used in Germany for filling Zeppelins. For
calcium carbide is convenient and portable and acetylene, when it is
once started, as by an electric shock, decomposes spontaneously by its
own internal heat into hydrogen and carbon. The latter is left as a
fine, pure lampblack, suitable for printer's ink.

Napoleon, who was always on the lookout for new inventions that could be
utilized for military purposes, seized immediately upon the balloon as
an observation station. Within a few years after the first ascent had
been made in Paris Napoleon took balloons and apparatus for generating
hydrogen with him on his "archeological expedition" to Egypt in which he
hoped to conquer Asia. But the British fleet in the Mediterranean put a
stop to this experiment by intercepting the ship, and military aviation
waited until the Great War for its full development. This caused a
s